This invention relates to an alternating current electric circuit breaker that uses semiconductor diodes to facilitate circuit interruption and, more particularly, relates to a circuit breaker of this type that comprises separable main contacts for carrying continuous current through the circuit breaker and further comprises diodes into which the current is diverted upon opening of the main contacts during an interrupting operation.
When the main contacts of my circuit breaker are parted during an interrupting operation, an arc is immediately established between them; and the resulting arc voltage is used to divert the current from the main contacts into a low impedance path that shunts the main contacts and includes the series combination of a diode assembly and an isolating switch. When current starts to flow in the shunting path, the isolating switch is in the closed position; but after a short delay it is opened, causing an arc to develop between its then-separated contacts. Current passes through this shunting path via the arc until a first natural current zero occurs after arc-initiation, following which the usual recovery voltage transient builds up. This recovery voltage transient and the power-frequency voltage that succeeds it are applied across the previously-conducting shunting path, appearing principally across its diode assembly until the polarity of the voltage across this shunting path reverses.